Measure of X-inactivation escape in circulation Cd11b myeloid cells with age

Abstract

Sex-chromosomally driven differences in gene expression within microglia and other macrophages contribute to age-related disease. Of particular interest is age-related ‘sterile’ neuroinflammation which is more pronounced in females than males and may underlie sex differences in neurodegenerative disease prevalence. X-inactivation is an important dosage compensatory mechanism used to silence on of the two X-chromosomes in females. Maintenance of X-inactivation relies on epigenetic mechanisms, such as DNA hypermethylation. With aging, epigenetic machinery becomes dysregulated and several gene products escape X-inactivation. Our hypothesis is that X-chromosome DNA methylation will change with age in females in microglia within the brain and potentially in circulating macrophages as well, indicating escape from X-inactivation. To assay DNA methylation, we used Bisulfite Amplicon Sequencing (BSAS) of X-chromosomally-encoded immune mediators (Tlr7, Tlr8 Gpr34). Circulating Cd11b myeloid cells, close relatives of brain resident microglia were assayed initially using blood collected from male and female mice at young (6 mo) and old (25 mo) timepoints. Following red blood cell lysis, circulating Cd11b myeloid cells were isolated using magnetic-activated cell sorting (MACS). Cell input and Cd11b+ cells were analyzed by flow cytometry prior to isolation of DNA for BSAS. BSAS analysis did not reveal any significant differences in methylation by age or sex indicating that these genes do not escape X-inactivation in this cell population. Future studies will examine microglia, a much longer-lived cell population and more potential candidate genes for escape from X-inactivation.